1. Field of the Invention
This invention relates to a spark timing (ignition timing) control system for a vehicle-driving internal combustion engine, and specifically relates to a spark timing control system designed so as to reducing the vibration of a vehicle. This invention also relates to a system for reducing the vibration of a vehicle through the control of a spark timing of a vehicle-driving engine.
2. Description of the Prior Art
In some vehicles, when a given decrease in the rotational speed of a vehicle-driving engine is required, the fuel supply to the engine is cut off. During a period after the fuel cutoff, when the fuel supply to the engine is restarted to accelerate the vehicle, the torque output of the engine abruptly increases so that the vehicle body tends to be exposed to a shock or an uncomfortable vibration.
Japanese published examined patent application 59-704, which corresponds to U.S. Pat. No. 4,373,489, discloses an engine spark timing control-system designed so as to reduce such a shock during the acceleration of the vehicle after the fuel cutoff. In the spark timing control system of Japanese patent application 59-704, during such an acceleration of the vehicle, the spark timing of a vehicle-driving engine is retarded from an optimal timing (a timing at which the engine output torque is maximized) to smooth an increase in the torque output of the engine. According to the prior art of Japanese patent application 59-704, the spark timing is controlled in response to only whether or not the engine is changing from the fuel cutoff state to the acceleration state.
In fact, the conditions of such a shock depend on not only whether or not the engine is changing from the fuel cutoff state to the acceleration state but also other various factors such as the engine load, the engine rotational speed, and the degree of the engine acceleration. Accordingly, in the spark timing control system of Japanese patent application 59-704, optimal spark timing control for reducing a shock tends to be difficult.
Japanese published unexamined patent application 1-121570 discloses a spark timing control system which includes a sensor for detecting a vehicle acceleration, a calculator for computing a variation in the detected vehicle acceleration, and a device for correcting a spark timing in accordance with the computed variation in the vehicle acceleration.